33^^ 



THE DOCxFISH. PHYLUM CHORDATA 



two roots join. The common nerve thus formed divides at once 

 into a short dorsal branch to the muscles and skin of the back, 

 and a long ventral branch to the rest of the segment. There is 

 also a short ramus communicans (plural rami communicantes) 

 to the sympathetic system. This is a series of connected ganglia, 

 approximately segmentally arranged, situated above the posterior 



M^^ 



'-olf.o. 



■sp. c. 



Fig. 255. — The brain of a dogfish, in ventral view. 



cer Cerebrum ; inf., return limb of infundibulum., constituting the ventral lobe of the pituitary body; 

 "/.I., lobi inferiores; m., medulla oblongata; n.i.l, neuro-intermediate lobe of pituitary body; 

 oif.l., olfactory lobe ; olf.o., olfactory organ ; op., ophthalmic branches of fifth and seventh nerves ; 

 sp.c. spinal cord ; s.v., saccus vasculosus ; II.-X., cranial nerves. 



cardinal sinus, and giving motor fibres to the viscera. Each fin 

 is supphed by a group of ventral branches formxing a plexus. 

 The detailed organisation of the nervous system is discussed in 

 Chapter 27. 



The cranial nerves (Figs. 256, 257), which arise inside the skull, 

 also have dorsal and ventral roots, and are also segmentally 

 arranged, but because their roots do not join, and because the 

 development of the sense capsules has obscured the segmentation 

 of the head, their proper plan was for long unrecognised and they 



